In present communications systems, each user is given a unique identifier, by means of which the true identity of the user is identified. The characteristic identifier is linked, for example, to a phone number of the user. The phone number is, in turn, associated with subscription profiles maintained by telecommunications service providers, such as mobile network operator. In communications networks phone numbers are used to identify the users, for example, for the purposes of charging and routing calls or delivering messages. The phone numbers are also used for other services, such as calling line indication, identification of a message sender and caller specific ringing tones. Also e-mail and IP (Internet protocol) addresses used in communications systems contain information useful for tracing the identity of the users of the system. An IP address contains numerical identification for individualising a data processor or a data transferring device connected to the Internet.
When a user of a mobile phone is for example calling another user of the communications system, the phone number of the caller is delivered to the called party, who may store the information of the phone number and use it for purposes unwanted by the caller. In some cases it is possible for the caller to prevent the delivery of the phone number for example, which in turn inhibits further communication between the parties. The called party cannot for example call back to the primary caller if the phone number is not delivered by the network or given by the caller.
Also in known electronic mail systems, when a user transmits an e-mail message, a return address is generated to be used by a recipient when sending a response. The return address is typically based on the user's account name. Consequently, the user's e-mail address cannot be changed without changing the user's account name. Additionally the account name and the corresponding e-mail address can reveal the user's identity to a certain extent. The e-mail addresses can be transferred from one person to another, even if the holder himself does not teach the e-mail address. E-mail and IP addresses are easily discovered and the true identities behind the addresses can be traced with little difficulty. Revealing e-mail or IP addresses to unwanted parties may cause considerable inconvenience in form of harassment e-mails and abuse of addresses.
In present communications systems, it is becoming increasingly important to protect the users true identities from being revealed to unwanted parties. It is also necessary for the communications system to be able to confidently and uniquely recognise the identity of the users in order to enable mutual communication between the relevant parties.